Tara Muth

A klippe of low-grade metasediments is exposed in northwest Bhutan, the base of which forms the erosional remnant of South Tibetan Detachment (STD) system. This detachment is an orogen-wide normal-sense shear zone that forms the upper boundary of the Greater Himalayan Sequence (GHS), the exposed metamorphic core of the Himalayas. Field mapping in this region of Bhutan is hindered by many factors such as access, high terrain, climate and logistics, and expense. Thus, many geological boundaries are insufficiently mapped and constrained. Due to high elevation, lack of vegetation and good exposure, this area is well-suited for mapping using remote sensing data. Here we examine the use of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) remote sensing data for geological mapping of a critical area of the Bhutan Hmalaya. Several techniques of ASTER data analysis were tested. The one found to be most suitable for mapping in the region was a combination of band ratio images. The main lithologies mapped using ASTER are: gneiss, leucogranite, metapelite, metacarbonate and shale. The first two belong to the footwall block (i.e. GHS) and the other three units to the hanging wall block of the STD. A structural analysis of the field data from the area is used to help constrain remote sensing mapping, determine the complex synformal geometry of the klippe, and construct geological cross-sections of the study area. Using the procedure developed for NW Bhutan, the northern Sikkim, which has never been visited by geologists, was mapped using ASTER data. This study has improved the geological map of largely inaccessible, yet geologically significant regions of the Himalayas and highlights the effectiveness of using remote sensing data as a geological mapping tool.

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Pages: 126
Supervisors: Djordje Grujic / Charlie Walls